Enhanced soft magnetic properties in multilayer structured amorphous Fe-Ta-C films

We report the investigation of enhanced soft magnetic properties in amorphous Fe-Ta-C thin films at larger thickness (similar to 200 nm), multistep magnetization reversal process and disappearance of magnetic disorder at low temperatures using [Fe-Ta-C(y)/Ta(x)] (n=0-4)/Fe-Ta-C(y) multilayer structured films prepared on thermally oxidized Si substrates. As-deposited films showed amorphous structure. Room temperature coercivity decreased largely from 24 Oe, for a single layer film, to 0.12 Oe, for multilayer films with n=4 with the same total Fe-Ta-C thickness, signifying that the intervening Ta layers play a critical role in reducing coercivity. Magnetic hysteresis loops for the multilayer films with n>2 exhibit pronounced multistep magnetization reversal processes for temperatures below 70 K depending on the number of multilayers and smooth narrow hysteresis curves for temperatures above 70 K. Low temperature thermomagnetization curves obtained under zero-field-cooled (ZFC) and field-cooled (FC) conditions showed a bifurcation between FC and ZFC data for the single layer film. With increasing the number of multilayers, the bifurcation point shifted to lower temperatures and almost disappeared for the multilayer film with n=4. The observed results are discussed on the basis of magnetostatic interaction effects between the Fe-Ta-C ferromagnetic layers. (C) 2011 American Institute of Physics. [doi:10.1063/1.3535417]